All of the signs added by this mod stack to 64, as contrasted with the vanilla signs, which stack to 16. One would expect them to stack to 16 like their vanilla counterparts.

I am guessing, looking at the code, that this goes all the way up to Terraform itself, but I was not able to find what part of terraform-wood-api handles the sign BlockItems.

This appears to have been fixed in Terrestria 2.1.5.